How to use python logging to log to files?

Question

I want to use the python logging facility to log output to different files (each module with its own log file). Therefore, I am adding something like the following to the begin of each python module see examples:

... other imports ...
import logging
logger = logging.getLogger('factory')
fh = logging.FileHandler('log/factory.log')
fh.setLevel(logging.DEBUG)
formatter = logging.Formatter('%(asctime)s %(levelname)s: %(funcName)s:%(lineno)d %(message)s')
fh.setFormatter(formatter)
logger.addHandler(fh)
... code ...

and then use logger.info("text") to log messages. However, no data is written to the file named log/factory.log although it is being created! The directory log exists and I have permission to write to that directory. Using the logging facility with basicConfig works fine...

You have to set the logging level also in the handler, as shown in the answer. See [this](http://stackoverflow.com/q/17668633/510937) question for more information. — Bakuriu, Jun 18 '14 at 20:04

nOOb cODEr · Accepted Answer · 2014-06-18T20:06:19.163

UPDATE

Looks like it's not logging because the logging level of the logger is set to logging.WARN. You must explicitly set the level on the logger to logging.DEBUG as well. I think the log/factory.log file is not being created because the log messages are not making it to that point yet. See http://dbgr.cc/v for a live demo of the code below:

import logging
import os

os.makedirs("log")

logger = logging.getLogger('factory')
fh = logging.FileHandler('log/factory.log')
fh.setLevel(logging.DEBUG)
formatter = logging.Formatter('%(asctime)s %(levelname)s: %(funcName)s:%(lineno)d %(message)s')
fh.setFormatter(formatter)
logger.addHandler(fh)

# notice that only the warning message is written
logger.debug("DEBUG MESSAGE")
logger.warn("WARNING MESSAGE")
logger.info("INFO MESSAGE")

with open("log/factory.log", "r") as f:
    print f.read()

# now update the level on the Logger to logging.DEBUG:
logger.setLevel(logging.DEBUG)

logger.debug("DEBUG MESSAGE")
logger.warn("WARNING MESSAGE")
logger.info("INFO MESSAGE")

with open("log/factory.log", "r") as f:
    print f.read()

Demo the code below at http://dbgr.cc/7:

import logging
import os

os.makedirs("log")

formatter = logging.Formatter('%(asctime)s %(levelname)s: %(funcName)s:%(lineno)d %(message)s')

# create logger with 'spam_application'
logger = logging.getLogger('factory')
logger.setLevel(logging.DEBUG)
fh = logging.FileHandler('log/factory.log')
fh.setLevel(logging.DEBUG)
fh.setFormatter(formatter)

# just so we can see things as they happen in stdout/stderr
ch = logging.StreamHandler()
ch.setLevel(logging.DEBUG)
ch.setFormatter(formatter)

# add the handlers to the logger
logger.addHandler(fh)
logger.addHandler(ch)

logger.debug("Debug log msg")
logger.info("Info log msg")
logger.warn("Warning log msg")

with open("log/factory.log", "r") as f:
    print f.read()

The key difference between your code and his is that you are setting the `fh` level, while he is setting only the `logger` level. You should highlight this difference. — Bakuriu, Jun 18 '14 at 20:05
Yes it is the 'global' logging level I forgot! I must have overlooked this in the example I have linked. I had the impresion, the level is set via `fh.setLevel(logging.DEBUG)` only... — Alex, Jun 18 '14 at 20:13

How to use python logging to log to files?

1 Answers1